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3.   Orthoformic ester and acetoacetic  ester  in  presence of
acetic anhydride form a hydroxymethylene ester (Claisen),
CH,                                   CH3
I    "                                    I
CO                                     CO
Clio + HC(OOCJLj)8   = C:CH.OCol-L; + 2CoH->OH,
I    -                    "                |
COOC2II5                          COOCjIIg
4.  The derivatives of acetosuccinic ester are very numerous
the compound lending itself readily to the formation of hetero-
cydic compounds (pyrrole, furfurane, thiophene, pyridine, &c.,
The impartial way in which acetoacetic ester was found to
behave, sometimes playing the part of a hydroxy-compottnd,
sometimes that of a ketone, has led to much discussion on the
merits of the formulre proposed by Geuther and Frankland,
CIL.C(OH):CIJ.COOC2II5.           CII:>CO.CHo.COOC2liri.
Geuther's formula.                                Frankland's formula.
From its physical properties and from its close analogy with
compounds which are known in both dcsmotropic forms, there
is now little doubt that the liquid is a mixture of both com-
pounds, the proportion of each being determined by tempera-
ture and other conditions. It is a typical example of 1automcr~
Monochloracetic Acid and Monobromacetic Acid. 
The action of chlorine on the aliphatic acids takes place in
presence of sunlight, also on the addition of small quantities of
the " halogen-carriers," iodine, sulphur, and red phosphorus. By
the action of iodine, I Cl is formed, which decomposes more readily
than the molecule of chlorine, and hydriodic acid is liberated,
The hydriodic acid is then decomposed by chlorine, and IC1
regenerated. Phosphorus acts by forming the chloride of
phosphorus from which the acid chloride is produced, which is
more readily attacked by chlorine than the acid. Sulphur
behaves in a similar fashion, sulphur chloride converting the
l For a full discussion of the subject of tautomer!sm, see the author's Organic
Chemistry for Advanced Students, E. Arnold, London.